1,721,012 research outputs found
Geochemical, mineralogical and Re-Os isotopic constraints on the origin of Tethyan oceanic mantle and crustal rocks from the Central Pontides, northern Turkey
No full textChromite, ultramafic and mafic rocks from Eldivan, Yapraklı, Ayli Dağ, Küre, Elekdağ and Kızılırmak in northern Turkey have been studied to determine their mineral and whole-rock geochemical, and Re-Os isotope geochemical characteristics. Most of the studied peridotites display depleted but commonly V-shaped chondrite-normalized rare-earth element (REE) patterns while some peridotites as well as pyroxenites from all areas exhibit light REE depleted patterns. Olivine (forsterite 82 to 92 mol%) and spinel (chromium number 13 to 63) in the studied peridotites exhibit a wide range of compositions. Compositions of spinels suggest that peridotites from Eldivan, Ayli Dağ and Küre experienced relatively large degrees of partial melting (~ 15 and 19 wt%), whereas those of the Kızılırmak area most likely reflect lower melting degrees (~ 4–6 wt%). Whole-rock and mineral chemical data indicate that the ultramafic rocks are similar to abyssal and supra-subduction zone peridotites. The ultramafic rocks of the investigated areas exhibit a wide range of 187Re/188Os (0.12 to 6.6) and measured 187Os/188Os (0.122–1.14), while the basaltic rocks from Küre, Eldivan and Kızılırmak areas have high 187Re/188Os (128–562) and measured 187Os/188Os (0.724–1.943). On the other hand, chromite from Eldivan, Elekdağ and Kızılırmak show high Os contents (21.81–44.04 ppb) and low 187Re/188Os (0.015–0.818) and 187Os/188Os (0.122–0.133). Re-Os model ages (TChur) for all analyzed samples yielded scattered ages ranging from Jurassic to Proterozoic. Overall, geochemical data are interpreted to reflect different degrees of partial melting, melt – rock interactions and metasomatic effects that produced a heterogeneous mantle in a supra-subduction setting
The Pilot Knob Iron Ore Deposits in Southeast Missouri, USA: A High-to-Low Temperature Magmatic-Hydrothermal Continuum
No full textThe Mesoproterozoic St. Francois Mountains igneous terrane in southeast Missouri, USA, contains eight major and several minor IOA/IOCG-type deposits. This study focuses on the Pilot Knob deposits, i.e., the largely massive Pilot Knob Magnetite (PKM) deposit and the Pilot Knob Hematite (PKH) deposit, which is located 240 m stratigraphically above the PKM and consists of variably mineralized bedded hematite and ore hosted in brecciated volcanic agglomerates. The PKM deposit was previously shown to be of magmatic and magmatic-hydrothermal origin, although its formation has not been precisely dated. The origin of the PKH deposit (i.e., sedimentary vs. hydrothermal) and its genetic relationship to the PKM, remain controversial.
We present new U-Pb data on apatite intergrown with massive magnetite in the PKM deposit and provide the first precise age for the formation of the PKM ore at 1437.7 ± 5.8 Ma. Petrographic observations of PKH ore, bulk rock compositions, and the mineral chemistry of hematite, which contains up to 2.7% Ti, suggest that the hematite in the PKH deposit crystallized from acidic and hypersaline hydrothermal fluids at a temperature between 200 and 250 °C. The Fe isotopic composition of 9 bedded (δ56Fe = 0.05-0.30‰, average 0.13‰) and 3 brecciated hematite samples (δ56Fe = −0.19 to 0.01‰, average −0.06‰) from the PKH deposit are slightly lighter than the published δ56Fe results of magnetite from the PKM deposit (δ56Fe = 0.06-0.27‰, average 0.17‰). However, all isotopic signatures fall within the magmatic range, indicating that iron in both deposits was originally sourced from a magma. Because of the hydrothermal origin of the PKH deposit, the iron isotopic compositions of the PKM and PKH ores that imply a shared/similar iron source, and the spatial proximity of both deposits, we argue that the PKM and PKH deposits are genetically related and represent two endmembers of a high-to-low temperature magmatic-hydrothermal continuum. In this scenario, ore fluids exsolved from the magma that facilitated the formation of the PKM deposit migrated upwards, infiltrated existing sedimentary structures near the surface, and precipitated hydrothermal hematite ore while preserving the original bedded and brecciated structures.
Geochemical signatures of the rhyolites/rhyodacites that host the PKM deposit imply that these rocks are A2-type felsic rocks that were emplaced in a post-collisional extensional setting. Bulk silicate Earth normalized patterns of the PKM deposit and wall rocks display a negative slope from Cs to Lu with negative Nb and Ta anomalies, indicating a hydrous source for the rhyolites and rhyodacites, possibly a subduction-modified subcontinental lithospheric mantle (SCLM). These geochemical signatures support a proposed tectonic setting of the St. Francois Mountains, wherein the igneous terrane developed on a growing continental margin. Episodic mafic-to-intermediate magmatism, and subsequently exsolved hydrothermal fluids, may have formed the cluster of IOA/IOCG-type deposits in the igneous terrane between ~1500 and ~1440 Ma. Within such a context, the PKM and PKH deposits may represent a shallow, small-scale snapshot of processes similar to the ones that form the IOA-IOCG continuum: a deeper magmatic event that exsolved a hydrothermal fluid that forms an overlying ore body
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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